Knockout driven fragmentation of porphyrins

Abstract

We have studied collisions between tetraphenylporphyrin cations and He or Ne at center-of-mass energies in the range 50-110 eV. The experimental results were interpreted in view of density functional theory calculations of dissociation energies and classical molecular dynamics simulations of how the molecules respond to the He/Ne impact. We demonstrate that prompt atom knockout strongly contributes to the total destruction cross sections. Such impulse driven processes typically yield highly reactive fragments and are expected to be important for collisions with any molecular system in this collision energy range, but have earlier been very difficult to isolate for biomolecules.

Decay pathways for protonated and deprotonated adenine molecules

“…Furthermore, we calculate the cross sections for heavy atom (carbon or nitrogen) knockouts in Rutherfordlike scattering processes by analysing the fragments formed in the collisions 27 . This has been shown to be an important non-statistical fragmentation pathway for stable and large molecular systems such as PAHs [27][28][29] , clusters 25,32,33 and porphyrins 34 in the velocity range considered here. The present model has been shown to overestimate the threshold energy for prompt atom knockout in collisions with helium 35 .…”

“…Previous studies 27,34,45 have shown that single or multiple atoms may be knocked out in atom-molecule collisions. The interplay between such prompt non-statistical fragmentation processes and statistical relaxation processes depends sensitively on the collision velocity, the atomic projectile mass and the stability of the target molecule.…”

DESIREE electrospray ion source test bench and setup for collision induced dissociation experiments

“…Some of these have lead to important new insights concerning molecular fragmentation mechanisms. Studies of fragmentations and energy-transfer mechanisms in native and hydrogenated PAHs [25][26][27][28][29][30][31] , fullerenes 32,33 and biomolecules 34,35,58 have been performed with the EIS-Lab setup for center-of-mass energies between 10 eV and 1 keV. In this region, nuclear stopping processes typically dominate the energy transfer to the molecule similar to what is believed to occur in supernova shockwaves 59,60 .…”

“…Experiments have been performed with this setup for a wide range of molecular ion projectiles, such as native and hydrogenated PAHs [25][26][27][28][29][30][31] , fullerenes 32,33 and biomolecules like tetraphenylporphyrin 34 and nbutylamine retinal protonated Schiff base 35 .…”

“…Typical center-of-mass collision energies range from roughly 10 eV to about 1 keV in these experiments, which among other things have revealed the importance of fast (subpicoseconds) single atom knockout processes 26,28,[32][33][34] .…”